1. Field of the Invention
The present invention relates to an improved method and apparatus for horizontal continuous casting of metal, particularly light metal, such as aluminum and its alloys.
2. Description of Prior Art
In horizontal continuous casting, a long ingot is usually produced by the following procedure. Molten metal is admitted into and maintained in a tundish. It is then fed via a refractory channel into a tubular chilled mold which is placed in a substantially horizontal position and which is drastically cooled. The molten metal is cooled in the tubular chilled mold so that the outer surface of the molten metal body forms a solidified shell. The molten metal body having the solidified shell is continuously withdrawn from the tubular chilled mold during cooling by directly impinging a coolant, e.g., water upon the metal body. During the continuous withdrawal, the solidification proceeds until the interior of the strand. The ingot produced may be cylindrical, rectangular, columnar, or hollow depending upon the shape of the mold.
Horizontal continuous casting inevitably involves various difficulties due to its inherent principle. The first difficulty results from the horizontal position of the mold. The molten metal in the mold presses against the lower part of the mold wall due to gravity, resulting in unbalanced cooling, i.e., strong and weak cooling at the lower and upper parts of the mold, respectively. Because of this unbalanced cooling, the center of the concave or convex solid-liquid interface where the solidification is completed, is liable to distort upward. In this case, the structure of the strand becomes non-homogeneous.
The second difficulty results from the lubricating oil introduced from the inner circumferential wall of the mold at its entry side to prevent the molten metal from sticking to the mold. If the lubricating oil is introduced uniformly from the entire inner circumferential part of the mold wall at its entry side, the lubricating oil is liable to flow down from the upper to lower inner circumferential part of the mold wall, resulting in a non-uniform lubricating surface.
The third difficulty also results from the horizontal position of the mold. Since the molten metal is in close contact with the lower part of the mold wall due to gravity, there tends to be insufficient clearance for the lubricating oil to flow in between the mold wall and the solidified shell. In the case of a poor lubrication, the solidified shell will break and the unsolidified molten metal will flow out through the break. The flow of molten metal, called "breakout", causes significant cast defects and, in a serious case, stops the casting operation.
Several proposals have been heretofore made to overcome the difficulties of horizontal continuous casting.
Japanese Examined Patent Publication (Kokoku) No. 39-23710 (U.S. Pat. No. 2,996,771) proposes to locate the orifice aperture of the mold for feeding the molten metal below the central axis of the mold.
Japanese Examined Patent Publication No. 45-41509 (U.S. Pat. No 3,455,369) proposes to fit an annular mandrel at the metal-entry aperture of the mold.
The proposals made in the above two Japanese patent publications disclose to direct downward the high-temperature stream of molten metal at the entry part of the mold, thereby mitigating the cooling at the lower part of the mold wall. These proposals are effective for aligning the solidification point, which is the most distant from the entry part of the mold, toward the central axis of the mold. Nevertheless, the above-described strong contact of molten metal with the lower part of the mold wall is not solved by these proposals. These proposals are, therefore, ineffective for obtaining a homogeneous cast structure.
Japanese Examined Patent Publication No. 46-28889 (U.S. Pat. No. 3,556,197) proposes a non-uniform distribution of the amount of lubricating oil at the upper and lower parts of the mold-wall. With this method, however, a uniform lubricating surface is difficult to form even when a considerably large amount of lubricating oil is supplied to the mold wall. In addition, the non-uniform distribution of lubricating oil results in cast defects, referred to as "oil folds", in the case of locally feeding an extremely great amount of lubricating oil.